11. Stock-based Compensation

The Company grants qualified and non-qualified stock options, RSUs, common stock and other stock-based awards under various plans to directors, officers, employees and other individuals. Stock options are granted at exercise prices of not less than the fair market value of the Company’s common stock on the date of grant. Additionally, the Company has an Employee Stock Purchase Plan (“ESPP”) that allows employees to purchase Company shares at a purchase price equal to 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last day of the offering period.

In February 2017, the Compensation Committee and the Board of Directors adopted, and in May 2017, the Company’s stockholders approved, an amendment to the Company’s Amended and Restated 2010 Long Term Incentive and Stock Award Plan (the “Long Term Incentive Plan”). The amendment (a) increases the number of shares of common stock issuable over the term of the plan by an additional 1,470,502 to 2,579,062 shares in the aggregate; (b) increases the number of shares of common stock issuable under the plan as incentive stock options by an additional 2,004,087 to 2,579,062 shares; (c) increases the per person award limits for purposes of compliance with Section 162(m) of the Internal Revenue Code to 2,000,000 shares for options and stock appreciation rights and to 2,000,000 shares for other types of stock awards; and (d) for purposes of Section 162(m) (i) confirms existing performance criteria upon which performance goals may be based with respect to performance awards under the Long Term Incentive Plan, and (ii) confirms existing means of adjustment when calculating the attainment of performance goals for performance awards granted under the Long Term Incentive Plan.

In February 2017, the Compensation Committee and the Board of Directors adopted, and in May 2017, the Company’s stockholders approved, an amendment to the Company’s 2015 ESPP. The amendment (a) increases by 250,000 the shares of common stock (from 15,000 shares to a total of 265,000 shares) available for issuance under the 2015 ESPP; and (b) increases the maximum number of shares of common stock an employee may purchase in any offering period to 2,500.

Stock Options

In February 2017, the Board of Directors approved a grant of 1,018,000 stock options to members of the Board of Directors, executives, and non-executive employees, subject to approval by the Company’s stockholders of an increase in the available shares under the Long Term Incentive Plan at the 2017 Annual Meeting of Stockholders. In May 2017, the shareholders approved the increase in the number of shares available for issuance under the Company’s Long Term Incentive Plan and 998,000 stock options were issued upon approval. As such, the stock options approved for grant in February 2017 were not deemed granted for accounting purposes until May 2017. The stock options granted to the non-employee board members and non-executive employees vest monthly over three years from the grant date. The stock options granted to the executives contain a combination of time-based and corporate performance-based vesting conditions. Stock-based compensation expense associated with the corporate performance-based stock options is recognized if the performance condition is considered probable of achievement using management’s best estimates. As of June 30, 2017, the achievement of certain corporate-based milestones was deemed probable and therefore the related expense is being recognized over the remaining service period. During the three months ended June 30, 2017, the Company recognized stock-based compensation expense of $0.2 million, related to stock options with performance-based vesting criteria.  

The stock options generally vest monthly over four years for employees and one year for directors. Stock options held by employees who qualify for retirement age (defined as employees that are a minimum of 55 years of age and the sum of their age plus years of full-time employment with the Company exceeds 70 years) vest on the earlier of scheduled vest date or the date of retirement. The fair value of the stock options granted during the three and six months ended June 30, 2017 and 2016, was estimated based on the following weighted average assumptions:

Stock option activity for the six months ended June 30, 2017, was as follows:

Of the stock options outstanding as of June 30, 2017, 412,500 were granted subject to performance objectives tied to the achievement of corporate goals set by the Compensation Committee of the Company’s Board of Directors and will vest in full or part based on achievement of such goals. As of June 30, 2017, the Company did not consider achievement of certain of the performance objectives to be probable and therefore the Company did not include any stock-based compensation expense for those stock options. As of June 30, 2017, the grant date fair value of awards outstanding for which the Company determined that it was not probable that it will achieve the goals was $0.7 million.

Restricted Stock Units

RSUs generally vest annually over three years for employees and one year for directors. RSUs held by employees who qualify for retirement age (defined as employees that are a minimum of 55 years of age and the sum of their age plus years of full-time employment with the Company exceeds 70 years) vest on the earlier of scheduled vest date or the date of retirement. The valuation of RSUs is determined at the date of grant using the closing stock price.

RSU activity for the six months ended June 30, 2017, is summarized below:

Stock-based Compensation Expense

The following table shows total stock-based compensation expense for stock options, RSUs and ESPP in the condensed consolidated statements of comprehensive income (loss) (in thousands):